Recently there have been various glasses-type video display devices in which video displayed on a display device such as a Liquid Crystal Display (LCD) is observed as a virtual image enlarged through an optical system having an eyepiece, a half mirror, or the like. Such glasses-type video display devices are called a wearable display. For example, WO2004/061519A1 (Patent Document 1) discloses an example of a wearable display.
Many video display devices are configured in such a way that they are worn on a head while wrapped around the head (called wearable displays). Such video display devices are mainly divided into a binocular type in which the video display system is formed at positions corresponding to eyes and a monocular type in which the video display system is formed at a position corresponding to one of the right and left eyes. Usually such wearable displays include a display unit which displays video and a headphone which supplies sound. Sometimes such wearable displays supply only video.
Many wearable displays which are worn on the head to display video to an eye of a user simultaneously include an output device formed by right and left headphones. In such wearable displays, it is investigated that a processing unit and the like for performing video output control, audio output control, and power supply control associated therewith are accommodated in the headphones. In the case where the processing unit and the like are accommodated in the headphones, a method in which the processing unit and the like are collectively accommodated in a headphone for one of the ears is adopted from the viewpoint of electric wiring distribution.
Headphones are widely used as an audio output device for listening to music.    Patent Document 1: WO2004/061519A1